Two-cycle scavenging system



Nov. 11, 1958 K. FROEHLICH 2,359,739

TWO-CYCLE SCAVENGING SYSTEM Filed July 25. 1956 4 Sheets-Sheet l 6yjar/reraq Uczrzer jtior'neyp Nov. 11, 1958 K. FROEHLICH 2,359,739

TWO-CYCLE SCAVENGING SYSTEM I Filed July 25. 1956 I 4 Sheets-Sheet 3Inventor furl Woe/dick 5y .FarZer 5 Carrier Jzzornega Nov. 11, 1958 K.FROEHLICH I 2,859,739

Two-cYcLE SCAVENGING SYSTEM Filed July 25. 1956 4 sheets-sheet 4Patented *Nov.-. 1 1, 1958 ice 2,859,739 TW r YCLE SCAYENGING SYSTEMKurt- Froehlibh; Milwaukee,"Wis.," assignor to Nordberg Manufacturing Copany Milwaukee, Wis., a corporation f- Wisc0nsin Application July 25;.19 6," Serial N0. 600,094

io ciaims. c1. 123-65 My invention is intheg field of internalcombustion engines and is anew and improved supercharging and/ orscavenging system-usable primarily ,on or with-twocycle engines. v I

.A primary .ohjectof -my,;invent;ion is a new and improvide twoacyclesupercharging system-for either diesel, dual-fuel or gas engines.

:Another object is ascavenging system for; two-cycle engines to lowerthe temperatureofthe cylinder charge.

Another object is agscavenging; and; supercharging system with animproved scavenging efliciency.

.Anotherpbject is. a scavenging system-tor two-cycle engines with aunique air movement during scavenging.

Another object .is a scavenging -and supercharging system fortwo-cycleengines which increases the effective stroke of thepistonabylowering -the exhaust and scavenging ports. v

Another object is a. scavenging and supercharging system forfltwo-cycleenginges which giyes ;a better or more effective blow-down:of theexhaust gases.

.Another. objectis a scavenging system for two-cycle engines which.reduces the cylinder mean temperature.

Other objects will appear from time to timevin the ensuingspecification, and ..drawings inwhich:

.Figure 1,-is a vertical-section through a two-cycle. enginewithmyinvention;

1 Figure. 2 is a section along. line 22 of Figure 1; .'Figure:3 is avsection alongline 3+3 of Figure 1; and

Figures 4, 5 and daresimilar to Figure 1, but on a reduced scale,showing itheoperation of the scavenging. system.

,.I n Figurevl. a: cylinder ltl with the usual liner 12 hasa suitable;cylinder ,head. 14-which -may be held onby bolts-1;6 or otherwise.*Thecylinder head may be provided with suitable openings or channels forvalves, fuel iniectors. and the like. For example-assuming that theengine .is a dual-fuel engine, a; tuelinjectorofany conventional typecouldbe positioned at 18, a gas valve atr20, and possibly a starting airvalve at 22, or suitable spark plug ,openingsrnightbeprovided if theengine is agas-fuled, spark-fired; engine. Be this as it may, thedetails of the auxiliary equipment, such -asthe fuel supply-system forthe cyli'nclen head, arenot important except.. to say that the inventionis .possibly most per-' tinent to a gas engine. I i

. .A pistont2 4pofv any suitable construction is provided ingthecylinder-to compress-the entrapped charge and exp'and through aworkingstrokewhen the cylinder contents-are ignited, byanysuitablemeans.

. a The scavenging system for the-cylinder includes two rows; of Iports, anv upper ontop, row, indicated 1 generally at,.26, and-alower orbottomrow, shown generally at .The inlet.. side, .designatedgenerally at'30,- may have a. suitable inlet manifold, .while. theexhaust side,designated, generallyati32, may have a suitableexhaustmanitold." Neitheris shown as" they may be conventional.

Regardless of the types ofmanifolds' or headers that are used, air at anelevated pressure, and possibly cooled, is supplied to the inlet sidefroma scavenging blower or a supercharger or both. Considering theloweror bottom row of ports in Figure 3 first, a box-or air chamber v334extending completely around the cylinder liner openson'the inletside 30and is closed to. the exhaust side so. that all of the .ports in thelower row .are.;inlet .or scavenging ports.

As shownin Figures 2;and;3,: the cylinder and liner are somewhatsymmetrical :about the center line 36. The ports 38 on each zsidetofxthecenter line on the inlet side of the engineare disposed at an. acute orsomewhat steep angle to the cylinder axis so. that the scavenging airwill have, a substantial vertical component of movement whenit,entersthe cylinder,*while the ports'40 on opposite sides of'the,;center. line. at the exhaust side of the enginearepracticallyatright angles to the cylinder axis. The inclination andrdisposition-of'these, ports .is probably best shown in Figure 1. .Movingcfrom thelateral .ports iii-around tottheasteeply inclined'ports 38, theinclination ofv the ports-.may .progressuniformly around each sideuntilthesteepestinclination is reached at the port 38. It should beunderstood'thatcorresponding ports symmetrically opposite each other.may be matched in inclination. At the same time, all of. the ports maybe directed. towards ascavengin'gaxis 42 which. is parallel to;but,-oflset-.ifrom the cylinder axis 44.

Turning to the upper row of ports aseshown in Figure 2, the inlet sideis; divided into-twosinlet-v passages or cavities 46 which aredisposed-symmetrically on each side of the center line136, eachbeingcontrolled by.a check valve 48 to prevent reverse scavenging.

'The ports in the upper row are .divided between inlet. and exhaustports. As Shown, the inlet ports may include the first three ports 50,52 and-54 on each side ofithe center line, and the lineof direction of:each of these inlet ports, sixin numbenamayalso-be directedat'thescavenging axis 42 andfdisposed ata. suitable inclination, each possiblybeing parallel to the inclination .of the scavenging ports below them.

The exhaust ports may include the ports designated 56, 53, 60 and 62arranged symmetrically on opposite sides of the center line 36 andseparated from the ,inlet passage by a suitable wallstructure .64 oneach side. The .inlet ports in ,thexupper, row are separated from thelower row inlet ports by suitable Walls 66 andi68, shown in Figure. 1,which are controlled-by the check valves. The upper edge of the inletports in the Upper or top row may all be in thesame lateral plane, designated generally at 70, which is slightly above the upper edge of theexhaust ports which may also be or fall in a common plane,designatedgenerally at 72, the distance being designated generally at74, sothat during the compression or upward stroke of thepiston, theexhaust ports will be covered before the inlet ports are fully closed sothat the cylinderawill receive a supercharge. By the same token, theexhaustports cover the majority of the port area of the top row of portsso that the contents of the cylinder will blow down rapidly at .the endof the pistons expansion stroke. I

The volume of the inlet passages from the opening into the cylinder backto the check valve, designated at 76, is reducedto a minimum by,movingthe check valve in as far as possible so that when the piston uncoversthese ports during its power stroke, as little exhaustgas as possiblewill blow into the upper inlet cavities, before the pressure in thecylinder drops below the scavenging and supercharging pressure.

In Figures 4, 5 and 6, the operation of the scavenging system has beenshown. In Figure 4, the piston 24 is on its expansion stroke and onlythe upper row of ports has been uncovered. The high pressure gases inthe cylinder blow down through the exhaust ports, as indicated generallyby the arrow at 78, and the scavenging air from the inlet ports in theupper row enters as at 80 at a substantial angle to the cylinder axis82.

In Figure 5, the piston is at or near bottom dead center and the lowerrow of ports has been uncovered. The inlet or scavenging air from theports 40 on the exhaust side but in the bottom row moves in a more orless lateral direction as indicated by the arrow 84. The air enteringthrough the ports in the lower row on the scavenging or inlet side at.38-flows in at a substantial angle as at 86. The two currents collideinthe neighborhood of the point 88 and the resulting mixture current isdeflected upwardly into the top of the cylinder on the right side at 90.The air from the scavenging or inlet ports in the top row is deflectedas indicated by the arrow 92 into the top right pocket 90 of thecylinderto clean out the residual hot gases which might otherwiseremain. The cylinder head is domed or otherwise shaped as at 94 so thatthe gases flow across and clean out the left top pocket 96 beforereturning to the flat exhaust ports as at 98.

In Figure '6, the piston is shown on its compression stroke covering thelower row of ports and the cross current from the inlet ports on theexhaust side of the bottom row is cut 01f. The contents of the cylinderhave been cleaned or flushed out and a fresh charge of air is beingsupplied through the inlet ports in the upper row as'indicated generallyat 100. This stream of air returns to the original direction, such as inFigure 4, and the excess and the remaining products of combustion willexhaust at 102.

It should be noted that the scavenging air from the inlet ports in theupper row initially enters at a substantial angle to the cylinder axisand is primarily directed more toward the center of the cylinder. Whenthe piston uncovers the lower row of ports, a lateral current of airfrom the flat or perpendicular inlet ports on the exhaust side collideswith the current from the upper inlet ports and forces the scavengingair into the right top pocket. During the compression stroke, the lowerrow of ports will be covered and the air current from the inlet ports inthe upper row will resume its flow more toward the center of thecylinder. I think of the movement of the air from the inclined directionat 80 in Figure 4, to the almost vertical direction at 92 in Figure 5,back to the inclined direction at 100 in Figure 6, as a fan action whichserves to sweep the hot pockets of exhaust gases from the top of thecylinder.

The use, operation and function of my invention are as follows:

My scavenging system for two-cycle engines consists generally in havingtwo rows of ports around the cylinder wall, one above theother.Preferably 'the two rows of ports each extend completely around thecylinder. The lower row of ports is connected to the scavenging side andonly scavenging air enters through these ports. The upper row of portsis divided between inlet and exhaust ports, the majority being exhaustports, and the inlet ports in the upper row are used for both scavengingand supercharging. It is important that the upper row has more area forexhausting than for supercharging.

The scavenging pattern or air flow path is shown generally in Figure 1,and it can be seen that the fresh scavenging air enters from all sidesof the cylinder through the lower row of ports but moves first laterallyand then somewhat upwardly from the inlet ports 40 on the far side ofthe cylinder from the normal scavenging side. In effect, the scavengingair flows toward the scavenging axis 42 with a large lateral componentof movement and then axially upward to the top of the cylinder beforeturning across the top and coming down the opposite side of the cylinderto the exhaust ports in the upper row.

It is important that the majority of the area in the upper row of portsbe devoted to exhausting the products of combustion so that a quickblow-down can be achieved. I have found that by this arrangement theupper row of ports can be lowered somewhat while achieving the sameblow-down in less piston movement, thereby acquiring a longer expansionstroke at the same time which results in more power output at the crankshaft.

It is additionally important that the check valves for the scavengingand supercharging ports in the upper row be moved in as close to thecylinder liner as possible so that the blow-back volume at 76 isreduced. This re duces the temperature of the cylinder charge andresults in a substantial power increase.

Because the majority of the area of the ports in the upper row can bedevoted to exhausting the products of combustion, the scavengingefliciency of my cylinder will be increased. This is caused by thequicker release of the exhaust gases. I find that making the exhaustareas approximately 55-60% of the total port area in the upper row willincrease the scavenging efiiciency a substantial amount.

The fan action of the scavenging air serves to sweep the top of thecylinder of'hot spots. I have found that this air movement effectivelycleans the right and left upper corners of the cylinder, if cylinderscan be considered to have corners. In any event, the cross rush of airfrom the lateral inlet ports on the exhaust side serves to deflect thescavenging air into the opposite pockets and 96, which might otherwiseharbor hot spots of exhaust gas.

While I have shown and described a preferred form of my invention, itshould be understood that numerous modifications and changes can bemade, all within the scope of the invention. For example, the inventioncan be applied to two-cycle gas, diesel or dual-fuel engines. It can beused on scavenged engines alone or on supercharged engines, usingrelatively high inlet manifold pressures. I, therefore, wish that myinvention be unrestricted except as by the appended claims.

I claim:

1. In a two-stroke cycle internal combustion engine, a cylinder andcylinder head, a piston in the cylinder, a plurality of annularlyarranged scavenging inlet air ports in the cylinder, a second pluralityof annularly arranged ports in the cylinder in a plane adjacent thefirst plurality but toward the cylinder head, a substantial number ofthe ports in a group on one side of the cylinder in the second pluralitybeing exhaust ports with the remainder on the other side of the cylinderbeing scavenging inlet air ports, the scavenging inlet air ports in thefirst and second plurality and the exhaust ports in the second pluralitybeing so directed relative to the axis of the cylinder and relative toeach other such that the scavenging air will ascend on the other side ofthe cylinder axis adjacent the scavenging inlet air ports in the secondplurality and will descend on the said one side of the cylinder adjacentthe exhaust ports in the second plurality to exit'through such exhaustports.

2. The structure of claim 1 in which the scavenging inlet air ports inthe second plurality rise slightly above the exhaust ports in the secondplurality, and a scavenging check valve mechanism for the scavenginginlet air ports in the second plurality.

3. In a two-stroke cycle internal combustion engine, a cylinder,cylinder head and piston, and a scavenging system including inlet andexhaust sides on opposite sides of the cylinder, two rows of portsaround the cylinder wall, one above theother, the majority of the portsin the top row being in direct communication with the exhaust side andfunctioning as exhaust ports, substantially all of the ports in thebottom row and the remainder of the ports in the top row being in directcommunication with the inlet side and functioning as inlet ports, eachport in the bottom row having a corresponding port generally above it inthe top row, the inlet ports in the bottom row on the exhaust side beinglaterally disposed generally pfrpendicular to the cylinder axis, theinlet ports in the bottom row on the inlet side being substantiallyinclined at an angle to the cylinder axis, the intermediate inlet portsin the bottom row uniformly increasing in inclination to the cylinderaxis symmetrically around each side from the generally perpendicularinlet ports on the exhaust side to the substantially inclined inletports on the inlet side, each inlet port in the top row being generallymatched in inclination to the cylinder axis to the inclination of itscorresponding inlet port below it in the bottom row, all of the exhaustports in the top row being laterally disposed generally perpendicular tothe cylinder axis.

4. The structure of claim 3 in which the inlet ports in the top row riseslightly above the exhaust ports so that, during the compression stroke,the inlet ports will be fully closed after the exhaust ports and thecylinder will have a supercharge of air.

5. The structure of claim 4 in which a scavenging check valve mechanismis provided for the inlet ports in the upper row only.

6. In a two-stroke cycle internal combustion engine, a cylinder,cylinder head and piston, and a scavenging system therefor includinginlet and exhaust sides generally on opposite sides of the cylinder, tworows of ports around the cylinder wall, one above the other, themajority of the ports in the top row being in communication with theexhaust side and functioning as exhaust ports, substantially all of theports in the bottom row and the remainder of the ports in the top rowbeing in communication with the inlet side and functioning as inletports, each port in the bottom row having a corresponding port generallyabove it in the top row, the inlet ports in the bottom row on theexhaust side being laterally disposed generally at right angles to thecylinder axis, the inlet ports in both rows on the inlet side beingsubstantially inclined to the cylinder axis, all of the exhaust ports inthe top row being laterally disposed generally at right angles to thecylinder axis.

7. In a two-stroke cycle internal combustion engine, a cylinder,cylinder head and piston, and a scavenging system therefor includinginlet and exhaust sides generally on opposite sides of the cylinder, tworows of ports around the cylinder wall, one above the other, themajority of the ports in the top row being in communication with theexhaust side and functioning as exhaust ports, substantially all of theports in the bottom row and the remainder of the ports in the top rowbeing in communication with the inlet side and functioning as inletports, the inlet ports in the bottom row on the exhaust side beinglaterally disposed generally at right angles to the cylinder axis, theinlet ports on the inlet side being substantially inclined to thecylinder axis, all of the exhaust ports in the top row being laterallydisposed generally at right angles to the cylinder axis.

8. In a two stroke cycle internal combustion engine, a cylinder,cylinder head and piston, and a scavenging system therefor includinginlet and exhaust sides generally on opposite sides of the cylinder, tworows of ports around the cylinder wall, one above the other, themajority of the ports in the top row being in communication with theexhaust side and functioning as exhaust ports, substantially all of theports in the bottom row and the remainder of the ports in the top rowbeing in communication with the inlet side and functioning as inletports, the inlet ports in the bottom row being constructed to direct alateral and upward main air current offset in the cylinder adjacent theinlet side, the inlet ports in the top row rising slightly above theupper level of the exhaust port and being constructed to direct aninitial upward air current in the cylinder adjacent the inlet side at asubstantial angle to the cylinder axis during the pistons expansionstroke after it has uncovered the upper row of ports but before ituncovers the bottom row, all of the ports in both rows being constructedso that when both rows of ports are uncovered by the piston, the mainair current from the inlet ports in the bottom row will merge with andtend to deflect the initial air current from the inlet ports in the toprow into the top of the cylinder in a direction more generally parallelto the cylinder axis to fully scavenge the top of the cylinder andcylinder head.

9. In a two stroke cycle internal combustion engine, a cylinder,cylinder head and piston, and a scavenging system therefor includinginlet and exhaust sides generally on opposite sides of the cylinder, tworows of ports around the cylinder wall, one above the other, themajority of the ports in the top row being in communication with theexhaust side and functioning as exhaust ports, substantially all of theports in the bottom row and the remainder of the ports in the top rowbeing in communication with the inlet side and functioning as inletports, each port in the bottom row having a corresponding port generallyabove it in the top row, the inlet ports on the inlet side being moreinclined to the cylinder axis than the inlet ports on the exhaust side,all of the exhaust ports in the top row being laterally disposedgenerally at right angles to the cylinder axis.

10. In a two stroke cycle internal combustion engine, a cylinder,cylinder head and piston, and a scavenging system therefor includinginlet and exhaust sides generally on opposite sides of the cylinder, tworows of ports around the cylinder wall, one above the other, themajority of the ports in the top row being in communication with theexhaust side and functioning as exhaust ports, substantially all of theports in the bottom row and the remainder of the ports in the top rowbeing in communication with the inlet side and functioning as inletports, the inlet ports in the bottom row being constructed to direct alateral and upward main air current offset in the cylinder adjacent theinlet side, the inlet ports in the top row being constructed to directan initial upward air current in the cylinder adjacent the inlet side ata substantial angle to the cylinder axis during the pistons expansionstroke after it has uncovered the upper row of ports but before ituncovers the bottom row, all of the ports in both rows being constructedso that when both rows of ports are uncovered by the piston, the mainair current from the inlet ports in the bottom row will merge with andtend to deflect the initial air current from the inlet ports in the toprow into the top of the cylinder in a direction more generally parallelto the cylinder axis to fully scavenge the top of the cylinder andcylinder head.

References Cited in the file of this patent UNITED STATES PATENTS

